Britain on Wednesday became the first country to approve AstraZeneca and Oxford University's home-grown UK Covid-19 vaccine, adding an easy-to-manage shot to the arsenal of a nation desperate for pandemic relief.

Even so, scientists - and regulators in Europe, following the Brexit divorce - are sceptical, given confusion over trial results earlier that left experts questioning the robustness of the data.

How does the AstraZeneca shot's efficacy stack up to others?

The AstraZeneca/Oxford vaccine's overall efficacy in preventing symptomatic infections was 70.4 percent, compared with the 95 percent efficacy of the shot from Pfizer/BioNTech, the other vaccine approved in Britain.

Single-dose efficacy was pegged at 52.7 percent, Britain said on Wednesday, in guidance to health workers, though a UK medical adviser also said that one AstraZeneca dose should be 70 percent effective after three weeks...